1. Field of the Invention
The present invention relates to a liquid crystal display device having a liquid crystal layer in which liquid crystal molecules are twist-aligned at an angle of substantially 90°.
2. Description of the Related Art
There has been conventionally known a twisted nematic type liquid crystal display device in which liquid crystal molecules in a liquid crystal layer held between a pair of substrates are twist-aligned from one substrate toward the other substrate. As disclosed in Jpn. Pat. Appln. KOKAI Publication No. 88962-1994, in a TN type liquid crystal display device in which liquid crystal molecules are twist-aligned at an angle of approximately 90°, each polarizing plate is set on a front side which is an observation side of display of a liquid crystal cell including a twisted nematic liquid crystal layer and on a rear side which is an opposite side of the front side.
An optical axis of one of a transmission axis and an absorption axis of each of the pair of polarizing plates is positioned in a direction parallel with or perpendicular to a direction of aligning treatment applied to an aligning film of each substrate of the liquid crystal cell, and optical axes of the respective polarizing plates are arranged to be parallel with or perpendicular to each other. In the liquid crystal display device in which the optical axes of the respective polarizing plates are arranged in parallel with each other, dark display in which transmission of light is substantially prevented (normally black display) is obtained in a state where an electric field is not substantially applied to the liquid crystal layer (a normally state). Further, in the liquid crystal display device in which the optical axes of the respective polarizing plates are arranged to be perpendicular to each other, bright display in which light transmission becomes maximum (normally white display) is obtained in the normally state.
In the normally white display, in order to obtain dark display, a sufficiently intensive electric field is applied to the liquid crystal layer to rise the liquid crystal molecules in a direction vertical to the substrates, and the twisted alignment state is released, thereby obtaining dark display.
However, in the normally white display, since the liquid crystal molecules are strongly affected by an alignment restricting force by the aligning treatment applied to the aligning films in the vicinity of each aligning film provided on an inner surface of each substrate which is in contact with the liquid crystal to restrict alignment of the liquid crystal molecules, a so-called “anchoring effect” by which behaviors of the liquid crystal molecules are suppressed provokes a reduction in contrast at the time of application of the electric field mentioned above (at the time of on) or tone reversal in an intermediate tone, thereby resulting in a decrease in display quality.